One-step route to a hybrid TiO2/TixW1−xN nanocomposite by in situ selective carbothermal nitridation

Abstract

Metal oxide/nitride nanocomposites have many existing and potential applications, e.g. in energy conversion or ammonia synthesis. Here, a hybrid oxide/nitride nanocomposite (anatase/Ti_xW_1?xN) was synthesized by an ammonia-free sol–gel route. Synchrotron x-ray diffraction, complemented with electron microscopy and thermogravimetric analysis, was used to study the structure, composition and mechanism of formation of the nanocomposite. The nanocomposite contained nanoparticles (<5 nm diameter) of two highly intermixed phases. This was found to arise from controlled nucleation and growth of a single oxide intermediate from the gel precursor, followed by phase separation and in situ selective carbothermal nitridation. Depending on the preparation conditions, the composition varied from anatase/Ti_xW_1?xN at low W content to an isostructural mixture of Ti-rich and W-rich Ti_xW_1?xN at high W content. In situ selective carbothermal nitridation offers a facile route to the synthesis of nitride-oxide nanocomposites. This conceptually new approach is a significant advance from previous methods, which generally require ammonolysis of a pre-synthesized oxide.     

One-step synthesis of poly(2-hexadecyloxyaniline)/selenium nanocomposite Langmuir–Blogett film by in situ redox reaction

Poly(2-hexadecyloxyaniline)/selenium (Se) nanocomposite monolayer was successfully prepared by spreading 2-hexadecyloxyaniline (2-C₁₆OAn) on selenious acid aqueous solution without additional oxidant and reductant. The formation of Se nanoparticles and the polymerization of 2-C₁₆OAn in the monolayer occurred simultaneously. The results showed that the limiting area per repeat unit on selenious acid subphase was larger than that on pure water, which indicated the formation of poly(2-hexadecyloxyaniline)/Se nanocomposite monolayer at air/water interface. The amorphous spherical Se nanoparticles and triangular single-crystal ones in the Langmuir–Blogett (LB) films were formed at 20 ± 1 °C and 35 ± 1 °C, respectively. Poly(2-hexadecyloxyaniline)/Se nanocomposite LB films with excellent quality could be obtained on different substrates, indicating that the transfer ratio of monolayer was close to unity. Furthermore, poly(2-hexadecyloxyaniline)/Se nanocomposite LB films possessed high conductivity with the current of 10⁻⁵ A cm⁻¹.     

Preparation of alumina–silica–nickel nanocomposite by in situ reduction through sol–gel route

Ceramic based composites with dispersion of nano sized metal/metal carbide particles have generated wide technological interest for their improved mechanical properties — hardness, fracture strength as well as fracture toughness, superior electrical properties and magnetic properties. In the present investigation alumina–silica gels have been prepared along with nickel chloride and dextrose distributed in the nanometric pores of the gel. The gels are prepared with different molar proportions of alumina and silica containing 5 wt% of nickel chloride and 50 wt% excess dextrose. During heat treatment at a temperature of 9008C for half an hour in nitrogen atmosphere, nickel chloride is reduced to metallic nickel by in situ generated hydrogen in the silica–alumina matrix. X-ray analyses indicate that no nickel chloride reduction is possible upto 50 mol% silica in alumina–silica matrix. Beyond this range, higher the silica content, higher is the reduction of nickel chloride. The presence of metallic nickel has been substantiated further by SAD analysis. Particle size analysis based on X-ray diffraction as well as transmission electron micrograph shows the presence of nickel particles of size ,20 nm distributed in the alumina–silica nanocomposite.     

Preparation of alumina–silica–nickel nanocomposite by in situ reduction through sol–gel route

Ceramic based composites with dispersion of nano sized metal/metal carbide particles have generated wide technological interest for their improved mechanical properties — hardness, fracture strength as well as fracture toughness, superior electrical properties and magnetic properties. In the present investigation alumina–silica gels have been prepared along with nickel chloride and dextrose distributed in the nanometric pores of the gel. The gels are prepared with different molar proportions of alumina and silica containing 5 wt% of nickel chloride and 50 wt% excess dextrose. During heat treatment at a temperature of 900°C for half an hour in nitrogen atmosphere, nickel chloride is reduced to metallic nickel by in situ generated hydrogen in the silica–alumina matrix. X-ray analyses indicate that no nickel chloride reduction is possible upto 50 mol% silica in alumina–silica matrix. Beyond this range, higher the silica content, higher is the reduction of nickel chloride. The presence of metallic nickel has been substantiated further by SAD analysis. Particle size analysis based on X-ray diffraction as well as transmission electron micrograph shows the presence of nickel particles of size ∼20 nm distributed in the alumina–silica nanocomposite.     

Sinterability of β-SiAlON powder prepared by carbothermal reduction and simultaneous nitridation of ultrafine powder in the Al2O3-SiO2 system

Three types of -SiAlON (Si_{6 – z} Al _z O _z N_{8 – z} ) powder were prepared by the carbothermal reduction and simultaneous nitridation of ultrafine powders in the Al₂O₃-SiO₂ system. The ultrafine starting oxide powders, prepared using the vapour-phase reaction technique, were mixed with carbon powder and heated at 1400 °C for 1 h under flowing nitrogen to form -SiAlON and followed by heating at 570 °C for 1 h in air to remove residual carbon. The resulting powders contained only -SiAlON with z values of 1.63, 2.05, and 2.99. The relative density (bulk density/true density) of -SiAlON compacts pressureless sintered at 1800 °C for 1 h under flowing nitrogen increased with z and reached 89.9% at z = 2.99. When the -SiAlON compact with z = 2.99 was hot pressed at 1800 °C for 1 h under flowing nitrogen, a maximum relative density of 93.6% was achieved. Although this hot pressed compact contained a small amount of 15R-SiAlON in addition to -SiAlON, it possessed a small average grain size (typically 0.5 m diameter) and high Vickers hardness (19.2 GPa).     

A new route to synthesize La1?xSrxMnO3

Self-Propagating High-temperature Synthesis (SHS) was used to producecomplex oxides (La_1–x Sr _x MnO₃ with x = 0, 0.1 and 0.2), which are used as the cathode in solid oxide fuel cells (SOFCs). Thermodynamic predications and experiments show that La_1–x Sr _x MnO₃ can be prepared via SHS under moderate conditions from a mixture of La₂O₃ + SrO₂ + Mn, using either gaseous oxygen or solid NaClO₄ as the oxidant. Partial melting at the high combustion temperature increased product homogeneity. The electrical conductivity of the product was 180 S·cm^–1 at 1000°C in air, matching that of sample made by other synthesis processes. SHS enables a more economical production of La_1–x Sr _x MnO₃ than existing commercial processes.     

In vitro study of hydroxyapatite/polycaprolactone (HA/PCL) nanocomposite synthesized by an in situ sol–gel process

Hydroxyapatite (HA) is the most substantial mineral constituent of a bone which has been extensively used in medicine as implantable materials, owing to its good biocompatibility, bioactivity high osteoconductive, and/or osteoinductive properties. Nevertheless, its mechanical property is not utmost appropriate for a bone substitution. Therefore, a composite consist of HA and a biodegradable polymer is usually prepared to generate an apt bone scaffold. In the present work polycaprolactone (PCL), a newly remarkable biocompatible and biodegradable polymer, was employed as a matrix and hydroxyapatite nanoparticles were used as a reinforcement element of the composite. HA/PCL nanocomposites were synthesized by a new in situ sol–gel process using calcium hydroxide and phosphoric acid precursors in the presence of Tetrahydrofuran (THF) as a solvent. Chemical and physical characteristics of the nanocomposite were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FTIR) analyses. The results indicated that pure HA nanoparticles were well-incorporated and homogenously dispersed in the PCL matrix. It was found that the mechanical property of PCL was improved by addition of 20 wt.% HA nanoparticles. Furthermore, the biological property of nanocomposites was investigated under in vitro condition. For this purpose, HA/PCL scaffolds were prepared through a salt leaching process and immersed in a saturated simulated body fluid (SBF) after 3 and 7 days. It was found that a uniform layer of biomimetic HA could be deposited on the surface of HA/PCL scaffolds. Therefore, the prepared HA/PCL scaffolds showed good potential for bone tissue engineering and could be used for many clinical applications in orthopedic and maxillofacial surgery.     

Microstructure and mechanical properties of TiC/Ti–6Al–4V composites processed by in situ casting route

Abstract

TiC/Ti–6Al–4V composites containing various volume fractions of TiC were produced by induction skull melting and common casting utilising in situ reaction between titanium and carbon powder. The microstructure and room tensile properties of as cast and heat treated TiC/Ti–6Al–4V composites were investigated. Bar-like or small globular eutectic TiC were found in 5 vol.-%TiC/Ti–6Al–4V composite, whereas the equiaxed or dendritic primary TiC particles were found to be the main reinforcements in 10 and 15 vol.-%TiC/Ti–6Al–4V composites. The as cast TiC/Ti–6Al–4V composites have shown higher strength but lower ductility than those of monolithic Ti–6Al–4V alloy. The shape and fracture of TiC particles can strongly influence the fracture and failure of the composites, and so the ultimate tensile strengths and elongations of as cast composites reduce with the increase in volume fraction of TiC. TiC particles appear to be spheroidised, and titanium precipitation can be found within large TiC particles after heat treatment at 1050°C for 8 h, which can promote the resistance to fracture of composites. Therefore, the elongations of the composites increase significantly, and the ultimate tensile strengths also have marginal increase especially for the 10 and 15 vol.-%TiC/Ti–6Al–4V composites after heat treatment.     

Efficient SiO2/WO3–TiO2@rGO nanocomposite photocatalyst for visible-light degradation of colored pollutant in water

The photoactive SiO₂/WO₃–TiO₂@rGO nanocomposite was fabricated through sol–gel, microwave, and hydrothermal approaches for the photodegradation of methylene blue (MB) as an organic-colored pollutant. The nanocomposite photocatalysts were formulated by adjustment of the ingredients content to achieve efficient synergic effects on photocatalyst performance. The results exhibited that optimum amount of SiO₂ and rise in WO₃/TiO₂ ratio as well as incorporation of reduced graphene oxide in structure can be led to further efficiency of degradation under visible light. The effect of sunlight irradiation, pH of MB solution, MB concentration, and lamp distance on photodegradation reaction were also investigated. The best performance about 99.9% MB degradation was obtained based on using 0.3 g/L of optimum photocatalyst to remove the 5 ppm MB solution with pH of 5.41 during 3 h irradiation by visible-light source with 30 cm distance from MB solution. As well, results showed that photocatalyst performance under visible light is better than sunlight irradiation. The most favorable photocatalyst indicated surface area of 60.9 m²/g. Furthermore, the reusability test indicated a proper activity after three cycles under the same conditions. So, the introduced efficient visible photoactive SiO₂/WO₃–TiO₂@rGO nanocomposite can be considered as an appropriate potential to remove organic pollutants in colored effluents.

     

One-step and iterative thermo-mechanical treatments to enhance Σ3n boundaries in a Ti-modified austenitic stainless steel

The article discusses the results of a study on low-strain thermo-mechanical (one-step and iterative) processing to enhance Σ3 ⁿ boundaries in a Ti-modified austenitic stainless steel (alloy D9). Solution annealed (SA) specimens were subjected to 10% thickness reduction by rolling followed by annealing at 1173, 1223, and 1273 K for 0.5, 1, and 2 h. Anomalous grain growth with moderate increase in Σ3 ⁿ boundaries was observed after annealing at 1,173 K for 0.5 to 2 h. Prolific multiple twinning with minimum deviation of Σ3 and Σ9 boundaries from ideal orientation was achieved after annealing at 1,273 K for 0.5 to 2 h. A significant disruption in random boundary connectivity was obtained in these conditions due to the presence of large number of Σ3-Σ3-Σ9/Σ3-Σ9-Σ27 triple junctions. Iterative processing (up to 4 cycles) employing 10% thickness reduction followed by annealing at 1,273 K for 0.5 h revealed fluctuations in the evolution of Σ3 boundaries. The Σ3 fraction increased after 2nd and 4th iteration and there is a drop after 3rd iteration. This was attributed to the increased driving force for grain boundary migration due to dislocation pile-up at twin boundaries during earlier iterations. A two step iterative processing comprising of 10% deformation followed by annealing at 1,273 K for 0.5 h is the recommended thermo-mechanical processing to achieve enhanced fraction of Σ3 ⁿ boundaries (~73%) in alloy D9.     

Self-assembling ε-Fe2O3/SiO2 nanoparticles to nanoflakes with paramagnetic-class properties via a milling-etching route

In this work, the milling-etching route is designed to synthesize nanoflakes with high-content ε-Fe₂O₃ phase, which is environmental friendly and more desirable for energy-efficient mass production of ε-Fe₂O₃ phase than conventional thermal treatment methods. More strikingly, this product conforms to the characteristics of paramagnetic-class properties, and our study shows that the unique property derived from ε-Fe₂O₃ phase is intimately related to large lattice strain and a few of small grains of ε-Fe₂O₃ based on Rietveld method and the law of approach to saturation. Relaxivities confirm the paramagnetic-class product has the potential to become a candidate as contrast agent in magnetic resonance imaging application filed. Our work not only sheds light on the preparation of ε-Fe₂O₃ phase, but also enables a new insight into the development of functional ε-Fe₂O₃ material in practical magnetically-relevant applications.     

Responses of bone to titania–hydroxyapatite composite and nacreous implants: a preliminary comparison by in situ hybridization

The effect of two biomaterials on bone formation in vivo by in situ hybridization, was compared by using RNA probes complementary to collagen 1(I) RNA, osteonectin RNA and osteocalcin RNA. Holes were drilled into the midshafts of rat femurs. Titania–hydroxyapatite composite (THA) or nacre cylinders were implanted and the bone–implant regions collected 14 days after operation. Cuboidal osteoblasts, intensely labelled with the three probes, were seen to be lining the newly formed bone surrounding the THA implant. Between the implant and the new bone, a layer of un-labelled, apparently non-osteogenic cells was observed. By contrast, the nacre implant was bonded to the newly formed bone without any soft tissue interference. Osteoblasts lining the distal surface of the newly formed bone were stained with all three RNA probes, although weaker than in the THA sample. Some of the osteoblasts were flattened. We concluded from the appearance of the osteoblasts that the bone formation in the nacre samples had progressed beyond the phase of maximal synthetic activity. Around the THA implant, the labelling indicated that bone-forming activity was still high. It was concluded that the bioactivity of nacre was higher than that of THA.     

Growth of nano-α-Fe2O3 in a titania matrix by the sol–gel route

Nano--Fe2O3 in a titania matrix was prepared by the sol–gel route. The nanocomposites containing various sizes of -Fe2O3 were precipitated by the heat treatment of the dried gel in a temperature range 100–1200 °C. Differential thermal analysis of the TiO2–Fe2O3 system showed peaks at 325, 390 and 730 °C. The formation of anatase as well as the rutile phase of TiO2 and the growth of -Fe2O3 were predicted from the above peak analysis. These results were in agreement with the X-ray diffraction studies. The sizes of the nanoparticles were analysed by transmission electron microscopic studies. The Mossbauer spectra of TiO2–Fe2O3 nanocomposites showed paramagnetic and superparamagnetic doublets for all the specimens containing nanoparticles of -Fe2O3. The electron paramagnetic resonance study indicated the presence of a paramagnetic phase in the nanocomposite samples. © 1998 Chapman & Hall     

What triggers a microcrack in printed engineering parts produced by selective laser sintering on the first place?

The proximity of un-melted particles within Selective Laser Sintered (SLS) printed engineering parts made of Nylon-12 is found as a major triggering effect for cracking and ultimately failure. The numerical investigation, by means of the eXtended Finite Element Method (XFEM), was performed over samples with different arrangements of un-melted particles obtained experimentally. The onset and propagation of microcracks was simulated. This included inherently how the degree of particle melt (DPM) in SLS parts affects and controls both crack initiation and propagation. The results evidenced that a microcrack started invariably between the two closest un-melted particles in all numerical tests performed considering different arrangements of un-melted particles.     

Effect of water content in sol on optical properties of hybrid sol–gel derived TiO2/SiO2/ormosil film

Sol–gel derived TiO₂/SiO₂/ormosil hybrid planar waveguides have been deposited on soda-lime glass slides and silicon substrates, films were heat treated at 150 °C for 2 h or dried at room temperature. Different amounts of water were added to sols to study their impacts on microstructures and optical properties of films. The samples were characterized by m-line spectroscopy, Fourier transform infrared spectroscopy (FT-IR), UV/VIS/NIR spectrophotometer (UV–vis), atomic force microscopy (AFM), thermal analysis instrument and scattering-detection method. The refractive index was found to have the largest value at the molar ratio H₂O/OR = 1 in sol (OR means OCH₃, OC₂H₅ and OC₄H₉ in the sol), whereas the thickest film appears at H₂O/OR = 1/2. The rms surface roughness of all the films is lower than 1.1 nm, and increases with the increase of water content in sol. Higher water content leads to higher attenuation of film.     

Preparation and characterization of maleimide–polystyrene/SiO2–Al2O3 hybrid nanocomposites by an in situ sol–gel process and its antimicrobial activity

Inorganic–organic nanocomposites have unlocked new opportunities in the design of innovative materials and compounds with enhanced and unique properties, based on soft chemistry. In the present study, a hybrid nanocomposite of maleimide–polystyrene (PSMA) with SiO₂ and Al₂O₃ (PSMA-SA) was synthesized by means of the sol–gel approach in the presence of γ-aminotriethoxysilane (γ-APTES), in which tetraethoxysilane (TEOS) and aluminum isopropoxide (AIP) were used as precursors. The Michael reaction led to bonding between the PSMA and SiO₂–Al₂O₃, giving a stable cross-linked network that prevented aggregation and mechanical mixing of the nanoparticles. XRD and FTIR analysis confirmed the effects of the coupling agent in promoting the Michael reaction. Thermal properties of the hybrid nanocomposites were tested through TGA and DSC. SEM, TEM and optical tests confirmed the controlled morphology and optical transparency of the composites. Additionally, the hybrid nanocomposites showed excellent solvent resistance and antimicrobial activity against pathogenic bacteria such as Bacillus cereus and Escherichia coli.     

Na1/2Bi1/2TiO3-BaTiO3系陶瓷压电性?及弛豫相变研究

系统研究了（１－ｘ）Ｎａ１／２Ｂｉ１／２ＴｉＯ３－ｘＢａＴｉＯ３（ｘ＝０．０２、０．０４、０．０６、０．０８、０．１０）无铅压电陶瓷系统的相界、材料压电性能,弛豫特性及相变．这个系统的陶瓷材料具有Ｋｔ／Ｋｐ较大,频率常数比较高等特点．Ｘ－ｒａｙ衍射结构分析发现此系统的相界在０．０４＜ｘ＜０．０６之间;材料的一些主要性能在相界附近达到极值．利用介电系数－温度曲线,并结合热激电流曲线对此系统的弛豫性进行研究和分析;初步研究了各配方组成的铁电－顺电的相变过程,发现在一定的组成范围内,材料在由铁电相向顺电相的转变过程中经历了一个过渡相区．     

Synthesis by a soft chemistry route and characterization of LixNi1 ? xO (0 < x < 0.5) compounds: Behavior in molten carbonates

Li_xNi_{1 – x}O powders and Li_xNi_{1 – x}O/Au with 0 < x < 0.5 are synthesized by a soft chemistry route. Analysis of Li_xNi_{1 – x}O by XRD shows an evolution from NiO (0 < x < 0.3) to LiNiO₂ (0.3 < x < 0.5) structures. The stability of Li_xNi_{1 – x}O/Au (0 < x 0.5) compounds synthesized by soft chemistry is studied in molten (Li_0.52Na_0.48)₂CO₃ eutectic at 650°C, under the cathode atmosphere used in molten carbonate fuel cells (air/CO₂: 70/30). After a 48 h immersion, analysis by XRD of the lithiated nickel oxide shows that lithium ions diffuse from the oxide to the bulk of the melt. The major oxide detected at the surface of the sample has a composition very close to that of NiO formed in situ at the surface of a nickel foil. Hence, highly lithiated nickel oxides are not stable in the melt. Li_xNi_{1 – x}O is rapidly transformed confirming the very high stability of Ni(II) in the working conditions.     

Enhancing mechanical properties of styrene–butadiene rubber/silica nanocomposites by in situ interfacial modification with a novel rare-earth complex

In this study, a novel rare-earth complex, dithio-aminomethyl-lysine samarium (DALSm), was prepared and then was employed as activator, accelerator, cross-linker and interfacial modifier to improve the mechanical properties of SBR/silica nanocomposites. The results showed that 6 phr DALSm performed a higher vulcanization efficiency than the combination of 5 phr activator zinc oxide (ZnO), 2 phr stearic acid (SA), and 2 phr accelerator diethyl dithiocarbamate zinc (EDCZn). Meanwhile, the XPS and FTIR analysis of DALSm/silica model compounds confirmed that hydrogen bonds and coordination bonds could be formed between DALSm and silica during vulcanization process, which can effectively facilitate the homogenous dispersion of silica particles into SBR matrix and enhance the interface adhesion between rubber matrix and filler. As a consequent, the mechanical properties of SBR/DALSm/silica nanocomposites were substantially improved and much more excellent than those of the SBR/EDCZn/silica nanocomposites containing equivalent filler content. Based on the results of immobilized polymer layer, the reinforcing mechanism of DALSm in SBR/silica nanocomposites was analyzed.